Factors influencing the deposition of inhaled particles.
Because the initial deposition pattern of inhaled particles of various toxic agents determines their future clearance and insult to tissue, respiratory tract deposition is important in assessing the potential toxicity of inhaled aerosols. Factors influencing the deposition of inhaled particles can be classified into three main areas: (1) the physics of aerosols, (2) the anatomy of the respiratory tract and (3) the airflow patterns in the lung airways. In the physics of aerosols, the forces acting on a particle and its physical and chemical properties, such as particle size or size distribution, density, shape, hygroscopic or hydrophobic character, and chemical reactions of the particle will affect the deposition. With respect to the anatomy of the respiratory tract, important parameters are the diameters, the lengths, and the branching angles of airway segments, which determine the deposition. Physiological factors include airflow and breathing patterns, which influence particle deposition. Various lung models used in predicting particle deposition are reviewed and discussed. The air-way structures of various animal species are compared, showing the unique structure of the human lung compared to the animal species under study. Regional deposition data in man and dog are reviewed. Recent deposition data for small rodents are presented, showing regional difference in deposition with the right apical lobe having the highest relative deposition. (+info)
Plasma jet takes off.
Thanks to a series of joint research projects by Los Alamos National Laboratory, Beta Squared of Allen, Texas, and the University of California at Los Angeles, there is now a more environmentally sound method for cleaning semiconductor chips that may also be effective in cleaning up chemical, bacterial, and nuclear contaminants. The Atmospheric Pressure Plasma Jet uses a type of ionized gas called plasma to clean up contaminants by binding to them and lifting them away. In contrast to the corrosive acids and chemical solvents traditionally used to clean semiconductor chips, the jet oxidizes contaminants, producing only benign gaseous by-products such as oxygen and carbon dioxide. The new technology is also easy to transport, cleans thoroughly and quickly, and presents no hazards to its operators. (+info)
Single molecule physics and chemistry.
New experiments using scanning probe microcopies and advanced optical methods allow us to study molecules as individuals, not just as populations. The findings of these studies not only include the confirmation of results expected from studies of bulk matter, but also give substantially new information concerning the complexity of biomolecules or molecules in a structured environment. The technique lays the groundwork for achieving the control of an individual molecule's motion. Ultimately, this work may lead to such practical applications as miniaturized sensors. (+info)
Low-energy, Q-switched ruby laser iridotomies in Macaca mulatta.
Laser iridotomies have been pursued as a means of performing anterior segments surgery as a virtually noninvasive procedure. An ideal single laser pulse technique has been elusive. In this study, iridotomies in rhesus monkeys were produced with a single exposure to a Q-switched ruby laser pulse. The iridotomy formation was accompanied by acoustic wave generation, bubble formation, and explosive tissue disruption, evidence of a nonlinear laser-iris interaction. The average energies at which these iridotomies were produced ranged between 18 and 48 mJ, some of the lowest energies reported for a laser iridotomy. Corneal changes were observed both at the epithelium and at the endothelium in some, but not all, of the eyes exposed. The epithelial changes morphologically resembled nonlinear damage reported for transparent solids. Damage to physical materials has been attributed to stimulated Brillouin scattering, a mechanism that may also play a role at the cornea. Consideration of such phenomena should be a part of the clinical evaluation prior to exposure of a cornea to high-power laser pulses. Although the endothelial change was more difficult to analyze, a shock-wave effect could not be discounted. (+info)
On the use of computational fluid dynamics in the prediction and control of exposure to airborne contaminants-an illustration using spray painting.
Computational fluid dynamics (CFD) is employed to simulate breathing-zone concentration for a simple representation of spray painting a flat plate in a cross-flow ventilated booth. The results demonstrate the capability of CFD to track correctly changes in breathing-zone concentration associated with work practices shown previously to be significant in determining exposure. Empirical data, and models verified through field studies, are used to examine the predictive capability of these simulations and to identify important issues in the conduct of such comparisons. A commercially available CFD package is used to solve a three-dimensional turbulent flow problem for the velocity field, and to subsequently generate particle trajectories for polydisperse aerosols. An in-house algorithm is developed to convert the trajectory data to breathing-zone concentrations, transfer efficiencies and aerosol size distributions. The mesh size, time step, duration of the simulation, and number of particles per size interval are all important variables in achieving convergent results. (+info)
Computational fluid dynamics as a method for assessing fume cupboard performance.
A commercially available computational fluid dynamic (CFD) software program, specific for HVAC systems, was used to study the performance of an aerodynamic fume cupboard. The numerical results showed good qualitative agreement with physical measurements giving confidence in the CFD model to simulate and predict overall fume cupboard performance. However, there were some quantitative differences specifically around 'aerodynamic' features that could not be accurately simulated by the software code. The CFD model was clearly able to demonstrate differences in performance between good and bad cupboard designs, and show the importance of using rear baffles and lipfoils. It also showed the importance of good design features when a 'worker' was standing against the front edge or when there were draughts in front of the aperture. The computer model was used to simulate the gas tracer containment test method described in BS 7258 (1994) [Laboratory Fume Cupboards], and had a much greater sensitivity than the recommended physical measuring instruments. The results given in this paper demonstrate the potential for using a commercially available software package for the optimisation of fume cupboard design and testing. It also indicates the economy of using CFD compared with building a prototype and testing a model. (+info)
Contaminant dispersion in the vicinity of a worker in a uniform velocity field.
The transportation of gaseous contaminant from a low and moderate low impulse (momentum<1 m s(-1)) source to the breathing zone was studied in a uniform air stream flow. Results of the effects of the direction and the velocity of principal air flow, convection due to a human body, arm movement of a human being and the type of source on the concentration profiles are presented. Three important results were obtained. Firstly, for a given low and moderate impulse low impulse contaminant source in the near field of a worker, his/her orientation relative to the principal air flow direction is the most important factor in reducing occupational exposure, with an air velocity of about 0.3 m s(-1). Secondly, the effect of convection resulting from body heat on air flow was lower than expected. Thirdly, arm movements influence contaminant dispersion, and should be included when models assessing exposure are developed. The present data can also be used to validate existing computational fluid dynamic (CFD) models. (+info)
Life in transition: balancing inertial and viscous forces by planktonic copepods.
Copepods (1-10 mm aquatic crustaceans moving at 1-1000 mm s(-1)) live at Reynolds numbers that vary over 5 orders of magnitude, from 10(-2) to 10(3). Hence, they live at the interface between laminar and turbulent regimes and are subject to the physical constraints imposed by both viscous and inertial realms. At large scales, the inertially driven system enforces the dominance of physically derived fluid motion; plankton, advected by currents, adjust their life histories to the changing oceanic environment. At Kolmogorov scales, a careful interplay of evenly matched forces of biology and physics occurs. Copepods conform or deform the local physical environment for their survival, using morphological and behavioral adaptations to shift the balance in their favor. Examples of these balances and transitions are observed when copepods engage in their various survival tasks of feeding, predator avoidance, mating, and signaling. Quantitative analyses of their behavior give measures of such physical properties of their fluid medium as energy dissipation rates, molecular diffusion rates, eddy size, and eddy packaging. Understanding the micromechanics of small-scale biological-physical-chemical interactions gives insight into factors influencing large-scale dynamics of copepod distribution, patchiness, and encounter probabilities in the sea. (+info)